One of the long term barriers to Discrete Element Modelling (DEM) of particulates is the
lack of suitable test particles that can be used to validate the models. This report presents a
new approach which involves 3D printing test agglomerates with “tunable” properties to
overcome this barrier. Agglomerates were designed using various tools i.e. DEM and
Computer Aided Software’s (CAD) software’s, and printed using a wider range of 3D
printing techniques based on the properties required. The study was divided into three
categories for a better understanding of agglomerate behavior:
1. Agglomerate Breakage.
2. Agglomerate Disintegration and Dissolution.
3. Agglomerate Flow and Segregation.
The first three years of the project investigated agglomerate breakage experimentally using
the 3D printed structures and validating the results in the DEM simulations. The Polyjet
technique was used to print symmetrical or random agglomerate structures. The
agglomerate design was systematically varied in terms of structure and bridge strength and
tested under various standard breakage tests. Agglomerate deformation and breakage were
simulated in EDEM using the Timoshenko Beam Bond Model (TBBM) with bond
properties matching the 3D printed agglomerates. Qualitatively the DEM produced
accurate predictions of the macroscopic breakage behavior and quantitatively predicted the
compressive load during the initial deformation of the agglomerate.
Building upon the initial findings, in the fourth year, colors were introduced in the printing
process to produce 3D printed agglomerates with different color distributions and material
properties. This was to provide feasible and accurate control on loading direction and better
tracking of individual particle position after agglomerate breakage. The strain distribution
over the agglomerate structure was plotted for the first time. In an additional study, the
Binder Jetting technique was used to produce agglomerates where the strength could be
tuned by changing the liquid to powder saturation level.
In the fifth year, a more sophisticated approach was attempted to observe agglomerate
breakage from three dimensions using Digital Image Correlation (DIC). Preliminary results
demonstrated the agglomerate strain distribution from the experiment in the same way
typically observed in Finite Element Simulations. Stress visualization also proves to be a
viable technique in understanding complex particle breakage behaviors. The Vero Clear
material used in Polyjet printing was found to exhibit photoelastic properties. We presented
the first report of stress visualization and semi-quantification under low loads for 3D
printed particles with complex geometry.
Wettability analysis for particulate materials has relied on the Washburn theory that
assumes a particle bed as an array of parallel capillaries. However, the complexity and
tortuosity in real-life powder beds or other industrial porous media usually are not fully
considered. Thus, we 3D printed porous substrates building from simple to complex as
artificial models to represent porous particle beds for liquid imbibition study. With some
deviation between experimental results and theoretical predictions observed, we paved the
way for a new production method for reproducible models of irregular powder beds.